Made MFA mandatory for gem releases

[sue445]

Motivation

I want to make MFA mandatory for gem security (supply chain attack)

https://blog.rubygems.org/2022/06/13/making-packages-more-secure.html

What will change after merging this PR?

MFA is requested when rake release is running

$ bundle exec rake release

(snip)

You have enabled multi-factor authentication. Please enter OTP code.
Code:

Please enable MFA on own account 🙏 https://rubygems.org/settings/edit

[sue445]

I released v0.5.2 🚀